Define 'execution' as in 'before execution begins'

spec/Section 3 -- Type System.md

@@ -487,7 +487,7 @@ information on the serialization of scalars in common JSON and other formats.
 If a GraphQL service expects a scalar type as input to an argument, coercion is
 observable and the rules must be well defined. If an input value does not match
 a coercion rule, a _request error_ must be raised (input values are validated
-before execution begins).
+before _execution_ begins).
 
 GraphQL has different constant literals to represent integer and floating-point
 input values, and coercion rules may apply differently depending on which type
@@ -757,7 +757,7 @@ type Person {
 }
 ```
 
-Valid operations must supply a nested field set for any field that returns an
+Valid operations must supply a selection of fields for any field that returns an
 object, so this operation is not valid:
 
 ```graphql counter-example

spec/Section 4 -- Introspection.md

@@ -72,7 +72,7 @@ GraphQL supports type name introspection within any _selection set_ in an
 operation, with the single exception of selections at the root of a subscription
 operation. Type name introspection is accomplished via the meta-field
 `__typename: String!` on any Object, Interface, or Union. It returns the name of
-the concrete Object type at that point during execution.
+the concrete Object type at that point during _execution_.
 
 This is most often used when querying against Interface or Union types to
 identify which actual Object type of the possible types has been returned.

spec/Section 5 -- Validation.md

@@ -468,7 +468,7 @@ should be unambiguous. Therefore any two field selections which might both be
 encountered for the same object are only valid if they are equivalent.
 
 During execution, the simultaneous execution of fields with the same response
-name is accomplished by {MergeSelectionSets()} and {CollectFields()}.
+name is accomplished by {CollectSubfields()}.
 
 For simple hand-written GraphQL, this rule is obviously a clear developer error,
 however nested fragments can make this difficult to detect manually.